Specific Aims: We have shown that the n-3 polyunsaturated fatty acids (PUFAs) in fish oils, which prevent sudden cardiac death, like local anesthetics, inhibit the fast, voltage dependent Na+ currents (i.e., a voltage-dependent need for a more negative resting membrane potential to close and return the Na+ channels to a resting, activatable state). Aim 1. Too determine if the voltage sensitivity of this effect is sufficient to inhibit action potentials in partially depolarized zones of the heart, but not affect non-ischemic cardiomyocytes that retain their normal resign membrane potentials. If so, this could explain the role of the inhibition of INa by n-3 PUFAS in ischemia-induced sudden cardiac death. Aim 2. To determine in a human embryonic cell line, HEK 293t, expressing alpha-subunits of the human myocardial sodium channel (hH1alpha), if point amino acid mutations in D-1, S6- the location of the putative batrachotoxin (BTX) binding site- and D-IV, S6- the location of the putative local anesthetic (LA) receptor-block the action of the n-3PUFAs on the Na+ channel grating process. Similarities between effects of Las and n-3 PUFAs indicates this to be likely: a) Both displace BTX, a potent cardiac and neural poison, from its binding site on the activated state of the Na+ channel alpha- subunit by non-competitive inhibition. B) Both inhibit INa by prolonging the inactivated state of the Na+ channel. C) Both are potent anti-arrhythmic agents. D-IV, S6 is the putative site of the LA receptor an D-I, S6 is the site of BTX binding. A single amino acid mutation in these two regions of the alpha-subunit renders the channel insensitive to BTX and affect LA action on the Na channel. These studies will add to understanding of how n-3 PUFAs act at a molecular level to inhibit the INa in cardiac myocytes. This effect is important for the preention by these n-3 PUFAs of ischemia-induced fatal ventricular arrhythmias. With 250,000 Americans, and millions more world wide, dying annually from cardiac sudden death for which there is no current safe and effective prevention or therapy, this action of the PUFAs has potentially great public health benefit.